If the dev finally treat that scene like it never happens in the lesbian routes then I will be really dissapointed. I can understand Aria and Mark fucking like rabbits before she starts any of the lesbian paths in the game, even if it's your weird that Aria says she is in love with Angelica from the start but still fucks Mark every ocasion she gets. The momment Aria is in a relationship with Angelica, the fucking with Mark shouldn't happen, even if it's a farewell fuck, it seems like she doesn't care about Angelica. I mean, she got with the girl she wanted and what does she do? go and fuck Mark because reasons. I can understand it happening if you aren't in that path with Aria, but it doesn't make sense for her to betray Angelica trust that way. If Angelica had a say in if it happens or not I can understand it, but she doesn't. In the dom path she betrays her "mistress" and in the love path she betrays her lover by fucking another.
The moment they had sex and start as lovers, it doesn't became an affair, at least not to Aria, it is a relationship between both of them, what's even more Angelica already treats it like she is in a relationship with her, and she even stops her sister from going further with Aria, hell Aria does too, and then she goes and fucks mark, it doesn't makes sense.